1. Field of the Invention
The present invention relates to an image display device with a function of resolution-converting an input image and outputting the resultant image, and more particularly to an image display device capable of reducing a capacity of an image memory temporarily storing the input image during the resolution conversion.
2. Description of Related Art
Conventionally, by providing an imaging device converting an image to an electrical signal, for example a video camera or the like, with an image memory temporarily storing a captured image, a function of exerting effects of camera-shake correction, electronic zoom and the like is added. The camera-shake correction is such that camera-shake information of a videographer (user of the video camera) is acquired with a gyro sensor or the like, and on the basis of the information, part of the image is cut out, and in order to magnify or contract the cut-out part to a standard angle of view, pixel values are interpolated by using adjacent pixel values, so that the image is electrically magnified or contracted. Furthermore, the electronic zoom is such that part of the image is cut out and in order to magnify the cut-out part to a standard angle of view, short pixel values are interpolated by using adjacent pixel values, so that the image is electrically magnified.
FIG. 7 illustrates one example of a timing chart showing the memory address transition and the image input and output timing of an image memory of continuous three screens at the time of full screen display in a related art image display device. This example shows how an input image signal of horizontal 1920 pixels×vertical 540 lines is resolution-converted to an output image signal of horizontal 1440 pixels×vertical 540 lines.
The image memory is made up of a ring buffer, writing is indicated by a broken line, and reading is indicated by a solid line. The address of the image memory starts with 0, and every time one line is written, a value equivalent to the one line is added. When the address reaches the end of the image memory, the address returns to 0 as illustrated, and again, every time one line is written, a value equivalent to the one line is added. The address is held even after the processing of one screen is completed, and the processing of the next screen is continuously performed from an end address of the previous screen.
An input synchronization signal and an output synchronization signal are sent in synchronization with each other, and while an image is being written into the image memory, an image 1V-period before the relevant image is being read from the image memory. Namely, for example, a screen-1 written into the image memory for a period (t11 to t12) is resolution-converted and read from the image memory for a period delayed by 1V (t13 to t14). In this period (t13 to t14), a screen-2 of the next screen is written simultaneously. Similarly, in a period (t15 to t16), simultaneously with the writing of a screen-3, the screen 2 which is a screen immediately before the relevant screen 3 is read.
Furthermore, FIG. 8 shows, as an operational example in which the camera-shake correction is assumed in the related art image display device, how, with horizontal 1600 pixels×vertical 450 lines positioned at a central part thereof specified as an effective range, an input image resolution of horizontal 1920 pixels×vertical 540 lines is resolution-converted to an output image resolution of horizontal 1440 pixels×vertical 540 lines.
Furthermore, as another operational example in which the camera-shake correction is assumed in the related art image display device, FIG. 9 shows address transition and a image input and output timing of the image memory when the effective range is varied so as to be horizontal 1600 pixels×vertical 450 lines (an upper part of the screen), horizontal 960 pixels×vertical 360 lines (a center of the screen), and horizontal 1600 pixels×vertical 450 lines (a lower part of the screen) in order.
In either case shown in FIGS. 8 and 9, similar to the operational example shown in FIG. 7, an input synchronization signal and an output synchronization signal are sent in synchronization with each other, and while an image is being written into the image memory, an image 1V-period before the relevant image is being read. In these examples, while a writing period of the input image varies corresponding to a line position of the effective range image, a reading period does not vary and the images are outputted at constant output timing.